For me the biggest feature I would like to see is a snapshot or history of all notes through time. If I delete a note and change my mind, I can recover it. If within a note I want to revert back to what it was previously, I can backtrack through my changes.
Out of curiosity, have you ever had a look at slate.js? It looks really powerful.
Out of the suggested candidates, the one on task progress view would interest me the most.
In any case, great work on Inkdrop. It’s my go-to note taking app!